Louis Seymour Bazett Leakey (7 August 1903 – 1 October 1972) was a Kenyan-British palaeoanthropologist and archaeologist whose work was important in demonstrating that humans evolved in Africa, particularly through discoveries made at Olduvai Gorge with his wife, fellow palaeoanthropologist Mary Leakey. Having established a programme of palaeoanthropological inquiry in eastern Africa, he also motivated many future generations to continue this scholarly work. Several members of the Leakey family became prominent scholars themselves.

Another of Leakey's legacies stems from his role in fostering field research of primates in their natural habitats, which he saw as key to understanding human evolution. He personally focused on three female researchers, Jane Goodall, Dian Fossey, and Birutė Galdikas, calling them "The Trimates." Each went on to become an important scholar in the field of primatology. Leakey also encouraged and supported many other PhD candidates, most notably from the University of Cambridge. As well, Leakey played a role in creating organisations for future research in Africa and for protecting wildlife there.

When I think back... of the serval cat and a baboon that I had as pets in my childhood days—and that eventually I had to house in large cages—it makes me sad. It makes me sadder still, however, and also very angry, when I think of the innumerable adult animals and birds deliberately caught and locked up for the so-called 'pleasure' and 'education' of thoughtless human beings.

— Louis Leakey, By the Evidence, Chapter 4

Leakey's parents, Harry (1868–1940) and Mary (May) Bazett Leakey (died 1948), were Church of England missionaries in British East Africa (now Kenya). Harry was the son of James Shirley Leakey (1824–1871), one of the eleven children of the portrait painter James Leakey. Harry Leakey was assigned to an established post of the Church Mission Society among the Kikuyu at Kabete, in the highlands north of Nairobi. The station was at that time a hut and two tents. Leakey's earliest home had an earthen floor, a leaky thatched roof, rodents and insects, and no heating system except for charcoal braziers. The facilities slowly improved over time. The mission, a centre of activity, set up a clinic in one of the tents, and later a girls' school. Harry was working on a translation of the Bible into the Gikuyu language. He had a distinguished career in the CMS, becoming canon of the station.

Leakey had a younger brother, Douglas, and two older sisters, Gladys and Julia. Both sisters married missionaries: Gladys married Leonard Beecher, Anglican Bishop of Mombasa and then Archbishop of East Africa from 1960 to 1970; Julia married Lawrence Barham, the second Bishop of Rwanda and Burundi from 1964 to 1966; their son Ken Barham was later the Bishop of Cyangugu in Rwanda.

The Leakey household came to contain Miss Oakes (a governess), Miss Higgenbotham (another missionary), and Mariamu (a Kikuyu nurse). Leakey grew up, played, and learned to hunt with the native Kikuyus. He also learned to walk with the distinctive gait of the Kikuyu and speak their language fluently, as did his siblings. He was initiated into the Kikuyu ethnic group, an event of which he never spoke, as he was sworn to secrecy.

Leakey requested and was given permission to build and move into a Kikuyu~style hut at the end of the garden. It was home to his personal collection of natural objects, such as birds' eggs and skulls. All the children developed a keen interest in and appreciation of the pristine natural surroundings in which they found themselves. They raised baby animals, later turning them over to zoos. Leakey read a gift book, Days Before History, by H. R. Hall (1907), a juvenile fictional work illustrating the prehistory of Britain. He began to collect tools and was further encouraged in this activity by a role model, Arthur Loveridge, the first curator (1914) of the Natural History Museum in Nairobi, the predecessor of the Coryndon Museum. This interest may have predisposed him toward a career in archaeology. His father was also a role model: Canon Leakey co-founded East Africa and Uganda Natural History Society.